Burglar Alarm Control Keypad

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Figure 1

The circuit was designed to illustrate the operation of an electronic keypad to be utilized in the burglar alarm system by having five keys as the security syntax.

Keypad – a set of buttons arranged in a block which usually display digits and other symbols but not a complete set of alphabetic lettersLight Emitting Diode (LED) – a semiconductor diode that is commonly a source of light when electric current pass through itBurglar Alarm – one way of preventing break in’s into one’s property, not only to protect the possessions but the occupants as well; can prevent the havoc and disruption caused by theft and break-in’sBC547 –NPNsmall signal transistors designed for general purpose switching and amplification due to its low voltage, low current and three different gain selectionsCMOS4081 – a quad dual inputANDgate in a 14-pin package generally characterized with small fluctuation, very high impedance, outputs that can sink and source, one output can drive up to 50 inputs, high speed gate propagation time, high frequency, and low power consumption

In choosing the component to be used in this circuit, the types of keypads recommended are those with each key in a separate connection but with a common terminal. Like the 12-key keypad, there should be 13 terminals present and not the 7 or 8 terminal matrix type. This circuit may also go well with the modular burglar alarm system.

To start setting the keypad, 5 keys will be chosen as the code and will be connected to the points A, B, C, D, and E while the other keys are directed to point F and resistor R1 holds the common wire lead. Using the 4 keys, A, B, C, and D, the alarm can be set by pressing the keys in the right arrangement. The switch Q6 will turn ON when the current passes through resistor R11 while capacitor C1 and resistor R2 sets the time for about 10 seconds. Q6 receives its current through R12 provided on the base by the relay as it holds itself while being energized. This will cause theLEDs to light as the 12 V output switches fromOFFtoSETposition. For turningOFFthe alarm, correct combination of keys A, B, C, D, and E will have to be done again.

The operation opCMOS4081 is demonstrated by pressing the A key which will cause Pin 1 for a period of time to be high and will enable gate 1. This timing is set by R2 and C1. Similarly, as B key is pressed, it will induce Pin 3 to get high. The output enables gate 5 to get high by enabling gate 2 while it links itself via R3. This operation is inherited by the remaining gates as they function in the same way where each enables the succeeding gate and links itself through a resistor.

Q5 will switch ON when the code is keyed in correctly within the allotted time through Pin 10, which will then connect Q6’s base to the ground. This will cause the relay to de-energize and turnOFFQ6. Resistor R9 connects all the keys which are not attached to A, B, C, D, or E to the base of Q4. Q4 causes Pin 1 to get low if any one of the incorrect keys is pressed, which will then fail the process of code entry and disables gate 1. Q1, Q2, and Q3 will also cause Pin 1 to get low when C, D, and E are pressed out of order.

For a 12-key keypad, over 10,000 combinations of codes can be created while in 16-key keypad, over 40,000 codes can be created. The codes can be modified by altering the connections of the keypad. Failure on the code can be suppressed by restarting the code entry. If more wrong keys were connected to F key, it will provided more security, granted that larger keypad will be used.

The entry access control systems provide reliable functioning and helps in meeting the safety requirements of office building, hotel, factories, home, apartment and others. There’s a wide selection of keypad access control system that are used to restrict or allow the physical access of a person into an organization. ?t may come in standalone, compact or card based access control terminal which are user friendly and finds application in offices , residences and other organizations. Some of these would be door access control system which are used in offices, banks, prisons and other establishments. Another application is the electronic access control systems that comes with features like wiring connections, electric lock, external bell, external push switch, magnet contacts and alarms.

The keypads work on the basis that the person passing through the door would need to know the access code to gain entry. Keypads are found on many alphanumeric keyboards and on other devices such as calculators, combination of locks and telephones which require largely numeric input. . Electronic keypads can be used areas such as factory floor, machine control, process control, automation industry and for aircraft cockpit door locking systems. Other common applications as they offer more security features were in conjunction with electric devices and security accessories such as egress buttons break glass units and exit sensors. Electronic keypads have a convenient way of passing through a door where access is restricted.

Source:www.zen22142.zen.co.uk/Circuits/Alarm/pad.htm

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